Aerobic exercise

When we exercise at a normal pace, our cells get plenty of oxygen and sugar is broken down quickly and efficiently. However, during sprints or other over-exertions, there isn't enough oxygen to go around. In this case, our cells use glycolysis as their primary source of energy, As part of glycolysis, hydrogen from glucose is placed on NAD+ to form NADH. Normally, these hydrogen atoms are then transferred to oxygen to form water. If oxygen isn't available, the NADH builds up and there isn't enough NAD+ to continue using glycol-ysis to make ATP. That's where lactate dehy-drogenase steps in: it combines pyruvate and NADH, producing lactic acid and NAD+